Thin peripheral layer of enamel rod is:
Histologically it is seen as a thin layer covering the enamel rods. It is formed when the crystals of the rods meet the inter rod substance. Rod sheats are very high in organic matter which is proteins. These sheats do not have any apatite crystals. So, rod sheats are comparatively hypo mineralized areas of the enamel. They are darker than rods and are relatively acid-resistant. It is believed that rod sheats aid in reducing the stress on the rods.